To compare efficacy of treatment with 3TC/ZDV in combination versus the better of DDI monotherapy versus DDI/ZDV combination therapy in symptomatic HIV-1 infected children who have received prior antiretroviral therapy. To evaluate safety, tolerance, to correlate plasma RNA levels, drug resistance, therapeutic drug levels and to compare effect of various treatments. A virologic substudy will also be performed to look at drug resistance, clinical endpoints and disease progression.